Printing ink manufacturers produce many surface and laminating flexographic or gravure inks. They are made either by grinding the dry pigments/presscakes into the vehicles, or letting down the waterborne or solventborne bases with appropriate technology varnishes. In the first case, after being mixed into aqueous or solvent-based vehicles in the process of making bases or inks, the dry pigments or presscakes must be further dispersed by grinding. This grinding step generally requires that the pigments be ground for a period of hours using milling equipment, such as a ball mill or an attritor mill. In the second case, a substantial inventory of different bases is required for making different inks. It is thus a great advantage to develop “Solventless Universal Bases” that can be easily letdown into either waterborne or solventborne dispersions/inks without additional grinding. This not only reduces the costly and time-consuming grinding process, but also reduces the inventory cost by using one base for multi-ink systems. Because the solventless base is already well dispersed, the cost may be further reduced by eliminating bad grinding batches and reworks. The freeze/thaw stability problem can also be eliminated due to the solventless nature of the bases. Additionally, the shelf life of the solventless bases is extended dramatically compared to the liquid bases.
Several U.S. Patents (U.S. Pat. Nos. 5,084,573, 5,095,122, 5,298,076, and 5,347,014) described a number of “effect Pigments” that are stir-in pigments which can be added to a coating or ink system without additional grinding. “Effect pigments” are described as inorganic or organic pigments that show metallic, pearlescent and/or silky-luster effects. These patents, however, did not disclose the “non-effect pigments” such as the yellow, magenta, cyan, black process colors. Two other U.S. Patents (U.S. Pat. Nos. 5,554,217 and 5,648,408) described the use of stir-in pigments in the suspension or solution of high molecular weight organic material (coatings or inks). The stir-in pigments were prepared by the wet-milling process and contain organic pigments, inorganic fillers and additives such as texture-improving agents. The stir-in pigments in these two patents were intended for use in organic systems instead of water-based systems. None of them is prepared by a hot melt dispersion process. Commercially available solventless bases or pigment chips are based on acrylics, SMA and nitrocellulose (Product Brochures of Knight Colors, KVK USA, Penn Colors, RHB Dispersions). None of these commercially available pigment chips can be used in both solvent and water-based systems. None of the patents or literature disclosed the effect of resin hydrophilicity and hydrophobicity balance on the performance of solventless colorants. In addition, the preferred resins disclosed in this invention record provide dramatically improved pigment dispersion characteristics and improve the overall pigment efficiency. Compared to other resins, the preferred resins permit manufacturing of inks or coatings at lower pigment content but with improved color characteristics.